<!--
  - Copyright 2016-present the IoT DC3 original author or authors.
  -
  - Licensed under the Apache License, Version 2.0 (the "License");
  - you may not use this file except in compliance with the License.
  - You may obtain a copy of the License at
  -
  -      https://www.apache.org/licenses/LICENSE-2.0
  -
  - Unless required by applicable law or agreed to in writing, software
  - distributed under the License is distributed on an "AS IS" BASIS,
  - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  - See the License for the specific language governing permissions and
  - limitations under the License.
  -->

<template>
    <div class="waves">
        <slot />
    </div>
</template>

<script>
    class ShaderProgram {
        constructor(holder, options = {}) {
            options = Object.assign(
                {
                    antialias: false,
                    depthTest: false,
                    mousemove: false,
                    autosize: true,
                    side: 'front',
                    vertex: `
                            precision highp float;
                            attribute vec4 a_position;
                            attribute vec4 a_color;
                            uniform float u_time;
                            uniform vec2 u_resolution;
                            uniform vec2 u_mousemove;
                            uniform mat4 u_projection;
                            varying vec4 v_color;
                            void main() {
                              gl_Position = u_projection * a_position;
                              gl_PointSize = (10.0 / gl_Position.w) * 100.0;
                              v_color = a_color;
                            }`,
                    fragment: `
                              precision highp float;
                              uniform sampler2D u_texture;
                              uniform int u_hasTexture;
                              varying vec4 v_color;
                              void main() {
                                if ( u_hasTexture == 1 ) {
                                  gl_FragColor = v_color * texture2D(u_texture, gl_PointCoord);
                                } else {
                                  gl_FragColor = v_color;
                                }
                              }`,
                    onUpdate: () => {
                        // nothing to do
                    },
                    onResize: () => {
                        // nothing to do
                    }
                },
                options
            )
            const uniforms = Object.assign(
                {
                    time: {
                        type: 'float',
                        value: 0
                    },
                    hasTexture: {
                        type: 'int',
                        value: 0
                    },
                    resolution: {
                        type: 'vec2',
                        value: [0, 0]
                    },
                    projection: {
                        type: 'mat4',
                        value: [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1]
                    }
                },
                options.uniforms
            )
            const buffers = Object.assign(
                {
                    position: {
                        size: 3,
                        data: []
                    },
                    color: {
                        size: 4,
                        data: []
                    }
                },
                options.buffers
            )
            const camera = Object.assign(
                {
                    fov: 60,
                    near: 1,
                    far: 10000,
                    aspect: 1,
                    z: 100,
                    perspective: true
                },
                options.camera
            )
            const canvas = document.createElement('canvas')
            const gl = canvas.getContext('webgl', {
                antialias: options.antialias
            })
            if (!gl) return false
            this.count = 0
            this.gl = gl
            this.canvas = canvas
            this.camera = camera
            this.holder = holder
            this.onUpdate = options.onUpdate
            this.onResize = options.onResize
            this.data = {}
            holder.appendChild(canvas)
            this.createProgram(options.vertex, options.fragment)
            this.createBuffers(buffers)
            this.createUniforms(uniforms)
            this.updateUniforms()
            this.createTexture(options.texture)
            gl.enable(gl.BLEND)
            gl.enable(gl.CULL_FACE)
            gl.blendFunc(gl.SRC_ALPHA, gl.ONE)
            gl[options.depthTest ? 'enable' : 'disable'](gl.DEPTH_TEST)
            if (options.autosize) window.addEventListener('resize', () => this.resize(), false)
            this.resize()
            this.update = this.update.bind(this)
            this.time = {
                start: performance.now(),
                old: performance.now()
            }
            this.update()
        }

        resize() {
            const holder = this.holder
            const canvas = this.canvas
            const gl = this.gl
            const width = (this.width = holder.offsetWidth)
            const height = (this.height = holder.offsetHeight)
            const aspect = (this.aspect = width / height)
            const dpi = (this.dpi = devicePixelRatio)
            canvas.width = width * dpi
            canvas.height = height * dpi
            canvas.style.width = 100 + '%'
            canvas.style.height = 100 + '%'
            gl.viewport(0, 0, width * dpi, height * dpi)
            this.uniforms.resolution = [width, height]
            this.uniforms.projection = this.setProjection(aspect)
            this.onResize(width, height, dpi)
        }

        setProjection(aspect) {
            const camera = this.camera
            if (camera.perspective) {
                camera.aspect = aspect
                const fovRad = camera.fov * (Math.PI / 180)
                const f = Math.tan(Math.PI * 0.5 - 0.5 * fovRad)
                const rangeInv = 1.0 / (camera.near - camera.far)
                const matrix = [f / camera.aspect, 0, 0, 0, 0, f, 0, 0, 0, 0, (camera.near + camera.far) * rangeInv, -1, 0, 0, camera.near * camera.far * rangeInv * 2, 0]
                matrix[14] += camera.z
                matrix[15] += camera.z
                return matrix
            } else {
                return [2 / this.width, 0, 0, 0, 0, -2 / this.height, 0, 0, 0, 0, 1, 0, -1, 1, 0, 1]
            }
        }

        createShader(type, source) {
            const gl = this.gl
            const shader = gl.createShader(type)
            gl.shaderSource(shader, source)
            gl.compileShader(shader)
            if (gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
                return shader
            } else {
                gl.deleteShader(shader)
            }
        }

        createProgram(vertex, fragment) {
            const gl = this.gl
            const vertexShader = this.createShader(gl.VERTEX_SHADER, vertex)
            const fragmentShader = this.createShader(gl.FRAGMENT_SHADER, fragment)
            const program = gl.createProgram()
            gl.attachShader(program, vertexShader)
            gl.attachShader(program, fragmentShader)
            gl.linkProgram(program)
            if (gl.getProgramParameter(program, gl.LINK_STATUS)) {
                gl.useProgram(program)
                this.program = program
            } else {
                gl.deleteProgram(program)
            }
        }

        createUniforms(data) {
            const gl = this.gl
            const uniforms = (this.data.uniforms = data)
            const values = (this.uniforms = {})
            Object.keys(uniforms).forEach(name => {
                const uniform = uniforms[name]
                uniform.location = gl.getUniformLocation(this.program, 'u_' + name)
                Object.defineProperty(values, name, {
                    set: value => {
                        uniforms[name].value = value
                        this.setUniform(name, value)
                    },
                    get: () => uniforms[name].value
                })
            })
        }

        setUniform(name, value) {
            const gl = this.gl
            const uniform = this.data.uniforms[name]
            uniform.value = value
            switch (uniform.type) {
                case 'int': {
                    gl.uniform1i(uniform.location, value)
                    break
                }
                case 'float': {
                    gl.uniform1f(uniform.location, value)
                    break
                }
                case 'vec2': {
                    gl.uniform2f(uniform.location, ...value)
                    break
                }
                case 'vec3': {
                    gl.uniform3f(uniform.location, ...value)
                    break
                }
                case 'vec4': {
                    gl.uniform4f(uniform.location, ...value)
                    break
                }
                case 'mat2': {
                    gl.uniformMatrix2fv(uniform.location, false, value)
                    break
                }
                case 'mat3': {
                    gl.uniformMatrix3fv(uniform.location, false, value)
                    break
                }
                case 'mat4': {
                    gl.uniformMatrix4fv(uniform.location, false, value)
                    break
                }
            }
        }

        updateUniforms() {
            const uniforms = this.data.uniforms
            Object.keys(uniforms).forEach(name => {
                const uniform = uniforms[name]
                this.uniforms[name] = uniform.value
            })
        }

        createBuffers(data) {
            const buffers = (this.data.buffers = data)
            const values = (this.buffers = {})
            Object.keys(buffers).forEach(name => {
                const buffer = buffers[name]
                buffer.buffer = this.createBuffer('a_' + name, buffer.size)
                Object.defineProperty(values, name, {
                    set: data => {
                        buffers[name].data = data
                        this.setBuffer(name, data)
                        if (name === 'position') this.count = buffers.position.data.length / 3
                    },
                    get: () => buffers[name].data
                })
            })
        }

        createBuffer(name, size) {
            const gl = this.gl
            const program = this.program
            const index = gl.getAttribLocation(program, name)
            const buffer = gl.createBuffer()
            gl.bindBuffer(gl.ARRAY_BUFFER, buffer)
            gl.enableVertexAttribArray(index)
            gl.vertexAttribPointer(index, size, gl.FLOAT, false, 0, 0)
            return buffer
        }

        setBuffer(name, data) {
            const gl = this.gl
            const buffers = this.data.buffers
            if (name == null && !gl.bindBuffer(gl.ARRAY_BUFFER, null)) return
            gl.bindBuffer(gl.ARRAY_BUFFER, buffers[name].buffer)
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(data), gl.STATIC_DRAW)
        }

        createTexture(src) {
            const gl = this.gl
            const texture = gl.createTexture()
            gl.bindTexture(gl.TEXTURE_2D, texture)
            gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE, new Uint8Array([0, 0, 0, 0]))
            this.texture = texture
            if (src) {
                this.uniforms.hasTexture = 1
                this.loadTexture(src)
            }
        }

        loadTexture(src) {
            const gl = this.gl
            const texture = this.texture
            const textureImage = new Image()
            textureImage.onload = () => {
                gl.bindTexture(gl.TEXTURE_2D, texture)
                gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, textureImage)
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR)
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
                gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
            }
            textureImage.src = src
        }

        update() {
            const gl = this.gl
            const now = performance.now()
            const elapsed = (now - this.time.start) / 5000
            this.time.old = now
            this.uniforms.time = elapsed
            if (this.count > 0) {
                gl.drawArrays(gl.POINTS, 0, this.count)
            }
            this.onUpdate()
            requestAnimationFrame(this.update)
        }
    }

    export default {
        name: 'Particles',
        mounted() {
            const pointSize = 1.5
            new ShaderProgram(document.querySelector('.waves'), {
                texture:
                    '',
                uniforms: {
                    size: { type: 'float', value: pointSize },
                    field: { type: 'vec3', value: [0, 0, 0] },
                    speed: { type: 'float', value: 5 }
                },
                vertex: `
                            #define M_PI 3.1415926535897932384626433832795
                            precision highp float;
                            attribute vec4 a_position;
                            attribute vec4 a_color;
                            uniform float u_time;
                            uniform float u_size;
                            uniform float u_speed;
                            uniform vec3 u_field;
                            uniform mat4 u_projection;
                            varying vec4 v_color;
                            void main() {
                              vec3 pos = a_position.xyz;
                              pos.y += (
                                cos(pos.x / u_field.x * M_PI * 8.0 + u_time * u_speed) +
                                sin(pos.z / u_field.z * M_PI * 8.0 + u_time * u_speed)
                              ) * u_field.y;
                              gl_Position = u_projection * vec4( pos.xyz, a_position.w );
                              gl_PointSize = ( u_size / gl_Position.w ) * 100.0;
                              v_color = a_color;
                            }`,
                fragment: `
                              precision highp float;
                              uniform sampler2D u_texture;
                              varying vec4 v_color;
                              void main() {
                                gl_FragColor = v_color * texture2D(u_texture, gl_PointCoord);
                              }`,
                onResize(w, h, dpi) {
                    const position = [],
                        color = []
                    const width = 400 * (w / h),
                        depth = 500,
                        height = 3,
                        distance = 3
                    for (let x = 0; x < width; x += distance) {
                        for (let z = 0; z < depth; z += distance) {
                            position.push(-width / 2 + x, -30, -depth / 2 + z)
                            color.push(1, 1, 1, z / depth)
                        }
                    }
                    this.uniforms.field = [width, height, depth]
                    this.buffers.position = position
                    this.buffers.color = color
                    this.uniforms.size = (h / 400) * pointSize * dpi
                }
            })
        }
    }
</script>

<style lang="scss" scoped>
    canvas {
        display: block;
    }

    .waves {
        position: absolute;
        left: 0;
        top: 0;
        right: 0;
        bottom: 0;
    }
</style>
